1. Field of the Invention
The present invention is concerned with the extraction and recovery of zinc from zinc-bearing materials through a process carried out in a chloride-based medium by chlorinating the metals followed by changing the medium and performing electrowinning in a conventional sulfate electrolyte. This process also allows for the recovery of precious and other metals. The present invention further relates to a process for producing zinc oxide from a complex sulfide material, an apparatus for performing the process, and processes for recovering iron, copper, silver, and lead from a complex sulfide material. More particularly, the invention relates to a process of producing zinc oxide from such a complex sulfide material by, preferably, a leaching of the sulfide material with hydrochloric acid and oxygen, followed by precipitation of iron from the leach solution using calcium oxide, and cementation of lead, copper, silver, cadmium and cobalt using zinc dust. Zinc oxide may then be precipitated from the leach solution using calcium oxide. The residual calcium chloride solution can then be treated with sulfuric acid to regenerate hydrochloric acid and produce gypsum.
2. Description of the Related Art
Use of chloride hydrometallurgy for the recovery of zinc from either complex sulfide ores or other metal-containing secondary materials offers many advantages over sulfate hydrometallurgical and pyrometallurgical processes. Concerns regarding the oversupplied market for sulfuric acid in North America and the shortage of conventional zinc concentrates have increased in recent years. Decoupling of zinc production from acid production and the processing of alternative feed materials offer a possible solution to these concerns. Gaining the ability to use a variety of zinc-bearing materials, such as difficult-to-process zinc concentrates or zinc containing wastes, has been the focus of numerous prior investigations. The recovery of precious metals from zinc concentrates and wastes, an unachievable task in some conventional electrolytic refineries, is another important objective.
Complex sulfide ores are characterized by a very high degree of mineral interlocking, and the enclosed minerals generally have small mineral grain size, making the production of saleable zinc and lead concentrates economically difficult or impossible using conventional mineral processing methods. Many deposits of this type are known and could be exploited if adequate processing technology were available.
The ferric chloride leach developed by Canmet (Craigen, W. J. S., Kelly, F. J., Bell, D. H. and Wells, J. A., Conf. Proc. Sulphide Deposits, pp. 255-69, June 1990, the contents of which are incorporated herein by reference) uses chlorine and ferric chloride to recover zinc from complex metal sulfides. A solution containing both zinc chloride and ferrous chloride is sent through a solvent extraction unit to remove iron and leave a clean zinc chloride solution, which is then sent to electrolysis to extract zinc and recover chlorine. However, this process is disadvantageous in that the cost of electrowinning zinc in chloride media is high compared to conventional sulfate electrowinning.
U.S. Pat. Nos. 4,378,275 and 4,536,214, the contents of which are incorporated herein by reference, provide a process for recovering zinc from complex sulfides. Complex sulfide ores are leached in autoclaves in one or two stages, and cupric chloride is the agent responsible for leaching zinc sulfide. The leach solution is purified by zinc dust cementation, and iron is removed by precipitation with MgO. Zinc is recovered by solvent extraction (i.e., loading di(ethylhexyl)phosphoric acid (DEHPA) and stripping by zinc sulfate electrolyte), followed by electrolysis. Recovery of reagents is accomplished by sending the resulting MgCl2 leach solution to a spray roaster, where HCl and MgO are regenerated. This process involves multiple steps to produce a clean, organic-free electrolyte for a conventional zinc sulfate cellhouse. Furthermore, autoclaves are capital intensive, with limited use in chloride media involving oxidative solubilization.
U.S. Pat. No. 4,082,629, the contents of which are incorporated herein by reference, sets forth a process that uses an autoclave to leach lead concentrates. The lead recovery section recovers lead chloride from a leach residue by calcium chloride leach, and then the end product (PbCl2) is sent to molten salt electrowinning.
In U.S. Pat. Nos. 4,337,128 and 4,465,569, the contents of which are incorporated herein by reference, a portion of the solution (a bleed) is treated with lime to precipitate zinc hydroxide. This product is contaminated with copper and iron hydroxide. The zinc hydroxide is separated from the solution and treated with FeCl2 and oxygen to recover ZnCl2 solution, which is purified and sent to zinc chloride electrowinning.
Additional processes have been used to extract metals from sulfide ores. In U.S. Pat. No. 4,026,773, the contents of which are incorporated herein by reference, a process for extracting metals, including zinc, from manganiferous ocean floor nodule ore is disclosed. The process comprises treating the ore with hydrochloric acid to produce a solution of the metal chlorides for further processing manganese dioxide by selectively extracting Fe, Cu, Ni, Co and Zn.
Similarly, in U.S. Pat. Nos. 4,206,023 and 4,346,062, the contents of which are incorporated herein by reference, zinc is recovered from materials containing zinc sulfide by partially chlorinating the zinc sulfide containing material in an aqueous medium.
U.S. Pat. No. 4,337,128 teaches a method of leaching sulfide-containing raw materials having metal sulfides of copper, iron, lead, silver, mercury and zinc. These raw materials are leached using a solution comprising cupric chloride and ferric chloride. The contents of U.S. Pat. No. 4,337,128 are incorporated herein by reference.
Copper and zinc are separated and recovered from aqueous chloride solutions containing lead, copper, zinc, and impurities in U.S. Pat. No. 4,362,607, the contents of which are incorporated herein by reference.
The contents of the following patents are also incorporated herein by reference: U.S. Pat. Nos. 4,440,569; 4,443,253; 4,505,744; 4,510,028; 4,545,963; 4,832,925; and 5,380,354. In these seven patents, zinc is recovered from zinc containing sulfidic materials that also contain iron and lead or silver by leaching the sulfidic material under oxidizing conditions.
Zinc may also be extracted from a sulfide ore or concentrate containing copper and zinc by subjecting the concentrate to pressure oxidation in the presence of oxygen and an acidic halide solution to obtain a pressure oxidation slurry, as shown in U.S. Pat. No. 5,869,012, the contents of which are incorporated herein by reference. This slurry is then subjected to a solid/liquid separation step to produce a liquor containing copper and zinc in solution.
Methods of purifying aqueous zinc solutions by using zinc dust to cement out impurities are also known. U.S. Pat. No. 4,637,832, the contents of which are incorporated herein by reference, discloses a method of cementing out impurities such as copper, cadmium, nickel, and cobalt from an aqueous solution of zinc sulfate by using zinc dust and an activator such as Cu—As or Cu—Sb.
It is desirable to develop a process for producing zinc oxide from complex concentrates of sulfide materials that is easy to perform and cost-effective. None of the above-mentioned techniques addresses a process of producing a clean zinc oxide that overcomes the problems noted above.